Gossip outbound stream is not yet opened on heartbeat

[Nashatyrev]

20:55:47.258 WARN  - Exception in gossipsub heartbeat
io.libp2p.core.InternalErrorException: Outbound gossip stream not initialized or protocol is missing
        at io.libp2p.pubsub.gossip.GossipRouterKt.getOutboundProtocol(GossipRouter.kt:40) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouterKt.getOutboundGossipProtocol(GossipRouter.kt:42) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.enqueuePrune(GossipRouter.kt:457) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.prune(GossipRouter.kt:442) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.heartbeat(GossipRouter.kt:371) [jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]

While the WARN log was fixed the stacktrace is suspicious: why gossip outbound stream is not opened on heartbeat? Normally outbound stream can be not yet opened at some moments when gossip initiated by a remote peer and immediately sending some message (see #160). But the outbound stream should be opened immediately and it's unlikely that during heartbeat it's not opened yet.

See the issue comment: Consensys/teku#2836 (comment)